The main goal of this proposal is to identify genes that are involved in "masking" maternal mRNAs in c. Elegans. A clever genetic screen, taking advantage of sem-2 mutants, was designed. The mutant, hermaphrodite animals are defective in egg expulsion and in consequence are killed by the larvae hatching inside. Further mutagenesis is expected to produce sterile survivors, defective in oogenesis and/or larvae development. It is assumed that some of the phenotypes will be due to mutations in genes responsible for masking of several known mRNAs. mRNA and protein plcalization will be used as an assay. The mutated "masking" genes will be identified by rescuing the mutations with injected cosmids from C.elegans library and further characterization of the genes involved. Repression of the gene activity by antisense RNA will be used to confirm the mRNA masking function of the identified gene.